Every time I have encountered this error code in the wild I have been extremely frustrated. Somebody tries to be cheeky, and rather than just return the proper status code (like a 429 or 503) they return this, which breaks a lot of HTTP status code parsing.
Not cheeky or funny. Boring actually. I know I'm boring but I have a job to do.
Honestly this discussion makes the occasional "I'm a teapot" seem useful. Your log and error handling ought to be capable of handling occurrences of a programmer doing something goofy.
A possibly apocryphal didactic story relevant because if an HTTP implementation misses 418, what else does it miss?:
The story goes that Van Halen had stipulated on their concert rider that they wanted M&M candy backstage, but with all the brown ones removed.
In his autobiography ‘Crazy From the Heat’ singer David Lee Roth explained this was not just a childish request, but in fact was a cunning test whereby he could tell instantly if the venue was safe or not.
He reasoned that if a concert venue did put brown M&Ms out, then they cannot have read the rider properly and that they then might also have made other more dangerous errors, such as in their electricity supply or stage weight capacity.
Not cheeky or funny. Boring actually. I know I'm boring but I have a job to do.